1. Field of the Invention
The present invention relates to a detector and a measuring device having the detector.
2. Description of Related Art
Conventionally, a detector for a measuring device is known. The measuring device includes a rod-like stylus having a contact, which is configured to contact an object to be measured (hereinafter “measured object”), at a tip portion thereof; a holding portion that holds a proximal end portion of the stylus; a body portion that supports the holding portion rotatably about a predetermined rotational axis; and a sensor that detects a rotational displacement of the holding portion. The measuring device detects a displacement of the tip portion of the stylus (hereinafter, simply referred to as a displacement of a stylus) based on the rotational displacement of the holding portion (See, for example, Related Art 1). A probe (detector) described in Related Art 1 includes a stylus, a stylus holder (holding portion), and a probe body (body portion), and detects a displacement of the stylus based on a rotational displacement of the stylus holder. A roundness measuring device having the probe moves the probe in a predetermined direction (hereinafter, “measuring direction”) to bring a gauge head (contact) of the stylus into contact with a measured object, thereby displacing the stylus, and measures the measured object based on the displacement of the stylus detected by the probe.
The probe described in Related Art 1 further has a contact switch to detect a rotation of the stylus holder in a direction opposite to the measuring direction. When the switch detects the displacement of the stylus in the direction opposite to the measuring direction, the roundness measuring device performs an operation, such as stopping the movement of the probe, etc., to prevent breakage of the probe caused by a collision with the measured object. However, according to the probe described in Related Art 1, since the probe is required to have the additional switch, the number of components increases, and manufacturing costs increase. Moreover, since an additional space is necessary to provide the switch to the probe, the size of the probe increases. On the other hand, it is conceivable to prevent the breakage of the detector caused by a collision with an measured object, based on the displacement of the stylus detected by the sensor. By doing so, since the detector is not required to have an additional component, manufacturing costs can be reduced, and the detector can be downsized.
FIG. 6 is a schematic diagram illustrating a configuration of a conventional detector 100. As shown in FIG. 6, the detector 100 includes a rod-like stylus 100 having a contact 111, which is configured to contact a measured object, at a tip portion thereof; a holding portion 120 that holds a proximal end portion of the stylus 110; a body portion 130 that supports the holding portion 120 rotatably about a predetermined rotational axis P; and a sensor 140 that detects a rotational displacement of the holding portion 120. In FIG. 6, the body portion 130 is shown in phantom for purposes of illustration. The holding portion 120 is provided with an abutting member 121, a plate spring 122 and a support member 123. The abutting member 121 has a groove portion 121A on which the proximal end portion of the stylus 110 abuts. The plate spring 122 is positioned to face the abutting member 121 in a direction perpendicular to the axis of the stylus 110 and the rotational axis P (horizontal direction in FIG. 6), and serves as a biasing member that biases the proximal end portion of the stylus 110 against the groove portion 121A. The support member 123 supports the abutting member 121 and the plate spring 122, and is rotatably supported by the body portion 130. The sensor 140 is provided with a core 141 attached to the support member 123, and two coils 142 attached to the body portion 130. The sensor 140 detects a rotational displacement of the holding portion 120 by detecting a displacement of the core 141 using a differential transformation method.
FIGS. 7A and 7B are views each illustrating a state when the stylus 110 is brought into contact with the measured object W. FIG. 7A shows a state when the stylus 110 is brought into contact with the measured object W by moving the detector 100 in a direction (hereinafter, “contact direction”) perpendicular to the axis of the stylus 110 and the rotational axis P. FIG. 7B shows a state when the stylus 110 is brought into contact with the measured object W by moving the detector 100 along the axial direction of the stylus 110.
When the stylus 110 is brought into contact with the measured object W by moving the detector 100 in the contact direction, as shown in FIG. 7A, the stylus 100 is displaced, and the core 141 is displaced along with the rotation of the holding portion 120. Therefore, the sensor 140 can detect the displacement of the stylus 110 based on the rotational displacement of the holding portion 120. Accordingly, the measuring device can prevent breakage of the detector 100 caused by the collision with the measured object W, by performing an operation such as, for example, stopping the movement of the detector 100, when the displacement of the stylus 110 is greater than a predetermined threshold.    [Related Art 1] Japanese Patent Application Publication No. 2004-233131.
However, when the stylus 110 is brought into contact with the measured object W, by moving the detector 100 in the axial direction of the stylus 110, as shown in FIG. 7B, the stylus 110 is not displaced. Therefore, the sensor 140 cannot detect the displacement of the stylus 110. Accordingly, the measuring device cannot perform an operation such as stopping the movement of the detector 100, and thus cannot prevent breakage of the detector 100 caused by a collision with the measured object W.